I currently have a blog set up on my domain (eg domain.com), but I would like to move it and all of its contents to a subdomain (eg sub.domain.com). Is there anything I need to watch out for or modify? Is there a tool which might do this more easily?
I’m afraid of database issues (it will be using the database instance as it is now) or calls from within the blog itself not resolving.
Check out this word-press plugin: Backup and Move.
If you want to avoid any plugin, there is detailed tutorial available on WordPress Codex, it will take hardly 20 mins
http://codex.wordpress.org/Moving_WordPress
Try the Duplicator plugin.
Creates a complete snapshot of everything (files & DB) and zips it up for moving to new server (or sub domain in your case).
Just remember that, if you have non WordPress subdomains in the source server, it’ll also package those up too. Use the ‘filter’ option to exclude them.
http://wordpress.org/plugins/duplicator/